Multiple starting and ending positions for scheduled or autonomous uplink transmission in unlicensed spectrum

ABSTRACT

A method of operating a wireless communication device comprises identifying a first start position for performing uplink (UL) transmission in unlicensed spectrum during a first transmission time interval, performing UL transmission in the first transmission time interval (TTI) according to the first start position, identifying a second start position for performing UL transmission in unlicensed spectrum during a second TTI, wherein the first and second start positions correspond to different symbol offsets within the respective first and second TTIs, and performing UL transmission in the second TTI according to the second start position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of International PatentApplication No. PCT/IB2018/052006, filed Mar. 23, 2018, which claims thebenefit of U.S. Provisional Patent Applications Nos. 62/476,491 and62/476,553 filed on Mar. 24, 2017, and U.S. Provisional PatentApplication No. 62/479,973 filed on Mar. 31, 2017, the respectivedisclosures of which are hereby incorporated by reference.

TECHNICAL FIELD

The disclosed subject matter relates generally to telecommunications.Certain embodiments relate more particularly to concepts such asLicensed-Assisted Access (LAA), LTE uplink transmissions, autonomousuplink transmission, and short transmission time interval (sTTI).

BACKGROUND

The 3GPP work on “Licensed-Assisted Access” (LAA) intends to allow LTEequipment to also operate in the unlicensed radio spectrum. Candidatebands for LTE operation in the unlicensed spectrum include 5 GHz, 3.5GHz, etc. The unlicensed spectrum can be used as a complement to thelicensed spectrum or for standalone operation.

For the case of unlicensed spectrum used as a complement to licensedspectrum, devices connect in the licensed spectrum (primary cell orPCell) and use carrier aggregation to benefit from additionaltransmission capacity in the unlicensed spectrum (secondary cell orSCell). A carrier aggregation (CA) framework allows aggregation of twoor more carriers with the condition that at least one carrier (orfrequency channel) is in the licensed spectrum and at least one carrieris in the unlicensed spectrum. In a standalone (or completely unlicensedspectrum) mode of operation, one or more carriers are selected solely inthe unlicensed spectrum.

Regulatory requirements may prohibit transmissions in unlicensedspectrum without prior channel sensing, or they may impose transmissionpower limitations or maximum channel occupancy time. Because unlicensedspectrum is generally shared with other radios of similar or dissimilarwireless technologies, a so called listen-before-talk (LBT) method isgenerally applied. LBT involves sensing the medium for a pre-definedminimum amount of time and backing off if the channel is busy. Due tothe centralized coordination and dependency of terminal devices on thebase-station (eNB) for channel access in LTE operation and imposed LBTregulations, LTE uplink (UL) performance is especially hampered. ULtransmission is becoming more and more important with user-centricapplications and the need for pushing data to cloud.

Today, unlicensed 5 GHz spectrum is mainly used by equipmentimplementing the IEEE 802.11 Wireless Local Area Network (WLAN)standard. This standard is known under its marketing brand “Wi-Fi” andallows completely standalone operation in the unlicensed spectrum.Unlike LTE, Wi-Fi terminals can asynchronously access the medium andthus show better UL performance characteristics especially in congestednetwork conditions.

LTE uses OFDM in the downlink and discrete Fourier transform spread(DFTS) spread orthogonal frequency division multiplexing (OFDM)(DFTS-OFDM) (also referred to as single-carrier FDMA) in the uplink. Thebasic LTE downlink physical resource can thus be seen as atime-frequency grid as illustrated in Figure (FIG. 1 where each resourceelement (RE) corresponds to one OFDM subcarrier during one OFDM symbolinterval. The uplink subframe has the same subcarrier spacing as thedownlink and the same number of SC-FDMA symbols in the time domain asOFDM symbols in the downlink.

In the time domain, LTE downlink transmissions are organized into radioframes of 10 ms, each radio frame consisting of ten equally-sizedsubframes of length Tsubframe=1 ms as shown in FIG. 2. Each subframecomprises two slots of duration 0.5 ms each, and the slot numberingwithin a frame ranges from 0 to 19. For normal cyclic prefix, onesubframe consists of 14 OFDM symbols. The duration of each symbol isapproximately 71.4 μs.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 ms) in the time domain and 12 contiguous subcarriers in thefrequency domain. A pair of two adjacent resource blocks in timedirection (1.0 ms) is known as a resource block pair. Resource blocksare numbered in the frequency domain, starting with 0 from one end ofthe system bandwidth.

Downlink transmissions are dynamically scheduled, i.e., in each subframethe base station transmits control information about which terminalsdata is transmitted to and upon which resource blocks the data istransmitted, in the current downlink subframe. This control signaling istypically transmitted in the first 1, 2, 3 or 4 OFDM symbols in eachsubframe and the number n=1, 2, 3 or 4 is known as the Control FormatIndicator (CFI).

The downlink subframe also contains common reference symbols, which areknown to the receiver and used for coherent demodulation of e.g. thecontrol information. A downlink system with CFI=3 OFDM symbols ascontrol is illustrated in FIG. 3. The reference symbols shown in FIG. 3are cell specific reference symbols (CRS) and are used to supportmultiple functions including fine time and frequency synchronization andchannel estimation for certain transmission modes.

Uplink transmissions are dynamically scheduled, i.e., in each downlinksubframe the base station transmits control information about whichterminals should transmit data to the eNB in subsequent subframes, andupon which resource blocks the data is transmitted. The uplink resourcegrid is comprised of data and uplink control information in the PUSCH,uplink control information in the PUCCH, and various reference signalssuch as demodulation reference signals (DMRS) and sounding referencesignals (SRS). DMRS are used for coherent demodulation of PUSCH andPUCCH data, whereas SRS is not associated with any data or controlinformation but is generally used to estimate the uplink channel qualityfor purposes of frequency-selective scheduling. An example uplinksubframe is shown in FIG. 4. Note that UL DMRS and SRS aretime-multiplexed into the UL subframe, and SRS are always transmitted inthe last symbol of a normal UL subframe. The PUSCH DMRS is transmittedonce every slot for subframes with normal cyclic prefix, and is locatedin the fourth and eleventh SC-FDMA symbols.

From LTE Rel-11 onwards, DL or UL resource assignments can also bescheduled on the enhanced Physical Downlink Control Channel (EPDCCH).For Rel-8 to Rel-10 only the Physical Downlink Control Channel (PDCCH)is available. Resource grants are UE specific and are indicated byscrambling the DCI Cyclic Redundancy Check (CRC) with the UE-specificC-RNTI identifier. A unique C-RNTI is assigned by a cell to every UEassociated with it, and can take values in the range 0001-FFF3 inhexadecimal format. A UE uses the same C-RNTI on all serving cells.

Scheduled LTE Uplink Scheme

In LTE the uplink access is typically controlled by eNB, i.e.,scheduled. In this case the UE would report to the eNB when data isavailable to be transmitted, e.g., by sending a scheduling requestmessage (SR). Based on this, the eNB would grant the resources andrelevant information to the UE in order to carry out the transmission ofa certain size of data. The assigned resources are not necessarilysufficient for the UE to transmit all the available data. Therefore, itis possible that the UE sends a buffer status report (BSR) controlmessage in the granted resources, in order to inform the eNB about thecorrect size and updated size of the data waiting for transmission.Based on that, the eNB would further grant the resources to carry onwith the UE uplink transmission of the corrected size of data.

In more detail, every time new data arrives at the UE's empty buffer,the following procedure is typically performed:

-   -   a. Using Physical Uplink Control Channel (PUCCH), the UE informs        the network that it needs to transmit data by sending a        Scheduling Request (SR) indicating that it needs uplink access.        UE has aperiodic timeslots for SR transmissions (typically on a        5, 10, or 20 ms interval).    -   b. Once the eNB receives the SR request bit, it responds with a        small “uplink grant” that is just large enough to communicate        the size of the pending buffer. The reaction to this request        typically takes 3 ms.    -   c. After the UE receives and processes (takes about 3 ms) its        first uplink grant, it typically sends a Buffer Status Report        (BSR) that is a MAC Control Element (MAC CE) used to provide        information about the amount of pending data in the uplink        buffer of the UE. If the grant is big enough, the UE sends data        from its buffer within this transmission as well. Whether the        BSR is sent depends also on conditions specified in 3GPP TS        36.321.    -   d. The eNB receives the BSR message, allocates the necessary        uplink resources and sends back another uplink grant that will        allow the device to drain its buffer.

Adding it all up, about 16 ms (+time to wait for PUCCH transmissionopportunity) of delay can be expected between data arrival at the emptybuffer in the UE and reception of this data in the eNB.

In case the UE is not RRC connected in LTE or lost its uplinksynchronization since it did not transmit or receive anything for acertain time, the UE would use the random access procedure to connect tothe network, obtain synchronization and also send the SR. If this is thecase the procedure until the data can be sent would take even longerthan the SR transmission on PUCCH.

Downlink Control Information (DCI) for Scheduling LTE UplinkTransmission

In the LTE system, the transmission formats and parameters arecontrolled by the eNB. Such downlink control information (DCI) typicallycontains:

-   -   Resources allocated for UL transmission (including whether        frequency hopping is applied).    -   Modulation and coding scheme    -   Redundancy versions    -   New data indicator    -   Transmit power control command    -   Information about demodulation reference symbol (DMRS)    -   In case of cross-carrier scheduling, the target carrier index is        also included.    -   Other applicable control information on UL transmissions

The DCI is first protected by 16-bit CRC. The CRC bits are furtherscrambled by the UE assigned identity (C-RNTI). The DCI and scrambledCRC bits are further protected by convolutional coding. The encoded bitsare transmitted from the eNB to UE using either PDCCH or EPDCCH.

Configuration of Special Subframe

Special subframe is defined for frame structure 2 for LTE and theconfiguration is illustrated by the following Table 1.

TABLE 1 Configuration of special subframe (lengths of DwPTS/GP/UpPTS)Normal cyclic prefix in downlink Extended cyclic prefix in downlinkSpecial UpPTS UpPTS subframe Normal cyclic Extended cyclic Normal cyclicExtended cyclic configuration DwPTS in uplink prefix in uplink DwPTSprefix in uplink prefix in uplink 0  6592 · T_(s) (1 + X) · 2192 · T_(s)(1 + X) · 2560 · T_(s)  7680 · T_(s) (1 + X) · 2192 · T_(s) (1 + X) ·2560 · T_(s) 1 19760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s)3 24144 · T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) (2 + X) ·2192 · T_(s) (2 + X) · 2560 · T_(s) 5  6592 · T_(s) (2 + X) · 2192 ·T_(s) (2 + X) · 2560 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 · T_(s)7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 · T_(s) — ——Licensed-Assisted Access (LAA) to Unlicensed Spectrum Using LTE

Up to now, the spectrum used by LTE is dedicated to LTE. This has theadvantage that LTE system does not need to care about the coexistenceissue and the spectrum efficiency can be maximized. However, thespectrum allocated to LTE is limited which cannot meet the everincreasing demand for larger throughput from applications/services.Therefore, Rel-13 LAA extended LTE to exploit unlicensed spectrum inaddition to licensed spectrum. Unlicensed spectrum can, by definition,be simultaneously used by multiple different technologies. Therefore,LTE needs to consider the coexistence issue with other systems such asIEEE 802.11 (Wi-Fi). Operating LTE in the same manner in unlicensedspectrum as in licensed spectrum can seriously degrade the performanceof Wi-Fi as Wi-Fi will not transmit once it detects the channel isoccupied.

Furthermore, one way to utilize the unlicensed spectrum reliably is totransmit essential control signals and channels on a licensed carrier.That is, as shown in FIG. 5, a UE is connected to a PCell in thelicensed band and one or more SCells in the unlicensed band. In thisdescription we denote a secondary cell in unlicensed spectrum aslicensed-assisted access secondary cell (LAA SCell). In the case ofstandalone operation as in MulteFire, no licensed cell is available foruplink control signal transmissions.

Unscheduled Uplink for LAA/MulteFire

For LTE UL channel access, both UE and eNB need to perform LBToperations corresponding to the scheduling request, scheduling grant anddata transmission phases. In contrast, Wi-Fi terminals only need toperform LBT once in the UL data transmission phase. Moreover, Wi-Fiterminals can asynchronously send data compared to the synchronized LTEsystem. Thus, Wi-Fi terminals have a natural advantage over LTEterminals in UL data transmission, and show superior performance incollocated deployment scenarios as seen in our simulation studies.Overall study results show that Wi-Fi has better uplink performance thanLTE particularly in low-load or less congested network conditions. Asnetwork congestion or load increases, the LTE channel access mechanism(TDMA type) becomes more efficient, but Wi-Fi uplink performance isstill superior.

In systems described in U.S. Provisional Patent Application No.62/326,292 and International Patent Application No. PCT/EP2016/062342,two different uplink concepts for LTE/LAA/MulteFire are proposed toincrease the flexibility and the performance of Uplink. In U.S.Provisional Patent Application No. 62/326,292, similar to Wi-Fibehavior, a UE can start the UL transmission without waiting forpermission from the eNB. In other words, a UE can perform LBT to gain ULchannel access whenever the UL data arrives without transmitting SR orhaving an UL grant from the eNB. The UE can use the unscheduled mode forthe whole data transmission or alternatively, transmits usingunscheduled mode for first N transmission bursts and then switches backto the eNB controlled scheduling mode. In International PatentApplication No. PCT/EP2016/062342, semi-persistent scheduling (SPS)grants with granted periodicity down to lms are proposed to achievesimilar behavior as autonomous uplink. With periodicity of 1 ms, a UEcan attempt to transmit every subframe for the whole granted period.

SUMMARY

In certain embodiments of the disclosed subject matter, methods areprovided for supporting multiple starting and ending positions forscheduled or autonomous UL transmission on unlicensed spectrum. Thus, UEhas flexibility to transmit UL at different starting positions based onLBT outcome.

One option is to define multiple starting/ending positions and ratematch the transmission based on available REs for a certainstarting/ending position. Another option is to adopt sTTI design onunlicensed spectrum.

Certain embodiments can be applied to LAA/NR-U/MulteFire or othertechnologies operating scheduled or autonomous UL transmission onunlicensed spectrum.

Certain embodiments are presented in recognition of shortcomingsassociated with conventional techniques and technologies, such as thefollowing examples. In LAA, scheduled UL on unlicensed spectrum followseNB scheduling regarding the starting and ending positions of an ULtransmission. The UE performs LBT before transmitting UL data. If LBTfails at the scheduled transmission starting point, UE will drop thetransmission and eNB treat it as NACK and schedule a retransmissionlater on. This leads to delay of UL transmission and impact the ULperformance. Also in LAA, autonomous UL transmission on unlicensedspectrum has fixed starting point for each subframe. The UE performs LBTbefore transmitting UL data. If LBT fails at the starting point, the UEwill drop the transmission for the subframe. This also leads to thedelay of UL transmission and impact the UL performance.

Certain embodiments may provide potential benefits compared toconventional techniques and technologies, such as the followingexamples.

-   -   Support of multiple starting positions for flexible and        efficient channel access on unlicensed spectrum    -   Reduce UL transmission delay and increase the overall system        performance    -   Enable efficient UL scheduling and transmission when multiple        starting/ending positions is supported.

In some embodiments of the disclosed subject matter, a method ofoperating a wireless communication device comprises identifying a firststart position for performing uplink (UL) transmission in unlicensedspectrum during a first transmission time interval (TTI), performing ULtransmission in the first TTI according to the first start position,identifying a second start position for performing UL transmission inunlicensed spectrum during a second TTI, wherein the first and secondstart positions correspond to different symbol offsets within therespective first and second TTIs, and performing UL transmission in thesecond TTI according to the second start position.

In certain embodiments, a symbol offset for the first start positioncorresponds to a symbol 0, and a symbol offset for the second startposition corresponds to a symbol 7.

In certain related embodiments, identifying the first start positioncomprises performing a first listen-before-talk (LBT) procedure, andselecting the first start position in response to a success of the firstLBT procedure, and identifying the second start position comprisesperforming a second LBT procedure, and selecting the second startposition as a consequence of a failure of the second LBT procedure.

In certain related embodiments, identifying the second start positioncomprises receiving an UL grant indicating that a symbol offset for thesecond start position corresponds to a symbol 7. In some suchembodiments, the method further comprises rate matching the ULtransmission to be performed in the second TTI based on availableresource elements (REs) for the second start position.

In certain related embodiments, the method further comprises identifyinga first end position for performing the UL transmission the first TTI,performing the UL transmission in the first TTI according to the firstend position, identifying a second end position for performing the ULtransmission the second TTI, wherein the first and second end positionscorrespond to different symbol offsets within the respective first andsecond TTIs, and performing the UL transmission in the second TTIaccording to the second end position. In some such embodiments,identifying the first end position comprises receiving an UL grantindicating the first end position.

In certain related embodiments, the first TTI is a short TTI (sTTI) andthe second TTI is a full-subframe or multi-subframe TTI. In some suchembodiments, the sTTI is a 7-symbol based sTTI or a 2-symbol based sTTI.

In certain related embodiments, the method further comprises selectingdifferent modulation and coding schemes (MCSs) for the UL transmissionsin the first and second TTIs according to the respective first andsecond start positions. In some such embodiments, the second startposition has a larger symbol offset than the first start position, andthe selected MCS for the UL transmission in the second TTI has a highermodulation order than the selected MCS for the UL transmission in thefirst TTI.

In some embodiments of the disclosed subject matter, a method ofoperating a wireless communication device comprises identifying multiplecandidate start positions and end positions for uplink (UL) transmissionin unlicensed spectrum, selecting start and end positions from among thecandidates, based on an outcome of a listen-before-talk (LBT) procedureperformed with respect to the unlicensed spectrum, and performing ULtransmission in the unlicensed spectrum using the selected start and endpositions.

In certain related embodiments, the selecting comprises determining thatat least one initial LBT attempt fails and at least one subsequent LBTattempt succeeds, and selecting start and end positions that correspondsto the at least one subsequent LBT attempt.

In certain related embodiments, the selecting comprises determining thatat least one initial LBT attempt fails, and declining to select startand end positions that correspond to the at least one initial LBTattempt.

In certain related embodiments, the method further comprises ratematching the UL transmission based on available resource elements (REs)for the selected start and end positions.

In certain related embodiments, the candidate start and end positionsfor UL transmission are defined in relation to a normal transmissiontime interval (TTI).

In certain related embodiments, the candidate start and end positionsfor UL transmission are defined in relation to a short transmission timeinterval (sTTI).

In certain related embodiments, the start and end positions follow UpPTSpositions defined for special subframe configuration for Frame structure2 in LTE.

In certain related embodiments, the outcome of the LBT procedurecomprises a successful LBT attempt in which the wireless communicationdevice gains access to a communication channel in the unlicensedspectrum.

In certain related embodiments, the method further comprises performingthe LBT procedure.

In certain related embodiments, the method further comprises receivingradio resource control (RRC) signaling that indicates the use of amultiple starting/ending position mode, and identifying the candidatestart and end positions as a consequence of receiving the RRC signaling.

In certain related embodiments, the method further comprises selecting amodulation and coding schemes (MCS) for the UL transmission according tothe selected start and end positions.

In some embodiments of the disclosed subject matter, a method ofoperating a radio access node comprises identifying a first startposition for an uplink (UL) transmission performed in unlicensedspectrum during a first transmission time interval (TTI), receiving theUL transmission in the first TTI according to the first start position,identifying a second start position for an UL transmission performed inunlicensed spectrum during a second TTI, wherein the first and secondstart positions correspond to different symbol offsets within therespective first and second TTIs, and receiving the UL transmission inthe second TTI according to the second start position.

In certain related embodiments, a symbol offset for the first startposition corresponds to a symbol 0, and a symbol offset of the secondstart position corresponds to a symbol 7.

In certain related embodiments, the first start position is identifiedin response to a first listen-before-talk (LBT) procedure successfullygaining access to a communication channel, and the second start positionis identified in response to a second LBT procedure failing to gainaccess to the communication channel

In certain related embodiments, the method further comprisestransmitting an UL grant to a user equipment (UE) to indicate that asymbol offset for the second start position corresponds to a symbol 7.

In certain related embodiments, the method further comprises identifyinga first end position for the UL transmission the first TTI, receivingthe UL transmission in the first TTI according to the first endposition, identifying a second end position for the UL transmission thesecond TTI, wherein the first and second end positions correspond todifferent symbol offsets within the respective first and second TTIs,and receiving the UL transmission in the second TTI according to thesecond end position. In some such embodiments, the method furthercomprises transmitting an UL grant indicating the first end position toa user equipment (UE). In some such embodiments, the first TTI is ashort TTI (sTTI) and the second TTI is a full-subframe or multi-subframeTTL The sTTI could be e.g. a 7-symbol based sTTI or a 2-symbol basedsTTI.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate selected embodiments of the disclosed subjectmatter. In the drawings, like reference labels denote like features.

FIG. 1 illustrates an LTE downlink physical resource.

FIG. 2 illustrates an LTE time-domain structure.

FIG. 3 illustrates a downlink subframe.

FIG. 4 illustrates an uplink subframe.

FIG. 5 illustrates licensed-assisted access (LAA) to unlicensed spectrumusing LTE carrier aggregation.

FIG. 6 illustrates multiple starting and ending positions for UL.

FIG. 7 illustrates examples of sTTI pattern.

FIG. 8 illustrates examples of sTTI for LAA UL.

FIG. 9 illustrates scheduling without a fixed time relationship betweengrant and UL transmission.

FIG. 10 illustrates a communication system according to an embodiment ofthe disclosed subject matter.

FIG. 11A illustrates a wireless communication device according to anembodiment of the disclosed subject matter.

FIG. 11B illustrates a wireless communication device according toanother embodiment of the disclosed subject matter.

FIG. 12A illustrates a radio access node according to an embodiment ofthe disclosed subject matter.

FIG. 12B illustrates a radio access node according to another embodimentof the disclosed subject matter.

FIG. 13 illustrates a radio access node according to yet anotherembodiment of the disclosed subject matter.

FIG. 14 illustrates a method of operating a wireless communicationdevice according to an embodiment of the disclosed subject matter.

FIG. 15 illustrates a method of operating a wireless communicationdevice according to an embodiment of the disclosed subject matter.

FIG. 16 illustrates a method of operating a radio access node accordingto an embodiment of the disclosed subject matter.

DETAILED DESCRIPTION

The following description presents various embodiments of the disclosedsubject matter. These embodiments are presented as teaching examples andare not to be construed as limiting the scope of the disclosed subjectmatter. For example, certain details of the described embodiments may bemodified, omitted, or expanded upon without departing from the scope ofthe disclosed subject matter.

The disclosed subject matter provides, among other things, methods andapparatuses to support multiple starting and ending positions forscheduled or autonomous UL transmission on unlicensed spectrum. Thefollowing description presents various embodiments in relation to LAAoperation as an example. However, the described concepts can also beapplied to LAA/NR-U/Multefire or other technologies performing scheduledor autonomous UL transmission on unlicensed spectrum.

Aspect 1: Multiple Starting/Ending Positions

In some embodiments, multiple starting and ending positions for ULtransmission on unlicensed spectrum are defined by eNB. A UE can startthe UL transmission on one of the defined starting positions. Oneexample is shown in FIG. 6, where two starting positions on symbol 0 and7 and two ending positions on symbol 12 and 13 are defined for LTE UL.The UE can start the UL transmission on either symbol 0 or symbol 7depending on LBT outcome. If LBT fails on symbol 0, the UE will continuesensing the channel and transmit on symbol 7 if LBT succeeds there. Inone other example, starting and ending positions of UL transmissionfollows the UpPTS positions defined for special subframe configurationfor Frame structure 2 in LTE.

The starting partial subframe for UL should be applied only for thefirst UL subframe in an UL transmission burst. This also applies for thefirst UL subframe sharing a maximum channel occupancy time (MCOT) withDL transmission. The subsequent subframes shall use the whole subframefor transmission.

In one example, the cell/carrier operating on unlicensed spectrum can beconfigured with “multiple starting/ending position mode” by eNB usingRRC signaling, indicating that UL transmission can start/end atdifferent positions and the UE has the flexibility to transmit UL on oneof the configured positions. In another example, an eNB signals one ofthe starting positions in Table 2 in UL grant in addition to RRCconfigured starting positions (i.e. symbol 0 and 7 in the example). IfUE transmits UL around symbol 0, the upper table applies and if UEtransmits UL around symbol 7, the following Table 2 applies.

TABLE 1 PUSCH starting position signaled in UL grant Value PUSCHstarting position around symbol 0 00 symbol 0 01 25 μs in symbol 0 10(25 + TA) μs in symbol 0 11 symbol 1 PUSCH starting position aroundsymbol 7 00 symbol 7 01 25 μs in symbol 7 10 (25 + TA) μs in symbol 7 11symbol 8

The eNB performs scheduling and link adaptation assuming a full subframetransmission although UL transmission can start on other positions thansubframe boundary. The UE rate matches the transport block size (TBS) toavailable REs based on the starting and ending position. Consequently,the code rate can be high if the starting positions is late in asubframe. To eliminate this, new modulation and coding scheme (MCS)entries can be introduced for an UL MCS table for partial startingsubframe. One principle is that UE uses a higher modulation order todecrease the code rate, similar to a DL partial subframe design for LAAprovided in 3GPP R1-163508. When transmitting partial starting subframeusing less than 13 symbols in UL, the new MCS entries shall be used.

In certain variations of aspect 1 for autonomous UL transmission, an eNBdefines multiple starting and ending positions for UL transmission onunlicensed spectrum, such as those illustrated in FIG. 6. A set ofsupported starting and ending positions is configured when the eNBactivates autonomous UL transmission, and the UE can start the ULtransmission autonomously on one of the configured starting positionsbased on LBT outcome. For instance, the UE can start the UL transmissionon either symbol 0 or symbol 7 depending on LBT outcome. If LBT fails onsymbol 0, UE continues sensing the channel and transmit on symbol 7 ifLBT succeeds there. In another example, starting and ending positions ofUL transmission follows the UpPTS positions defined for special subframeconfiguration for Frame structure 2 in LTE. In a further example,starting and ending positions of UL transmission follows sTTI pattern.In another example, the autonomous transmission always starts with areference symbol to mark the start of the transmission at the boundaryof any or subset of the DFTS-OFDM symbols within a subframe.

The starting partial subframe for UL is applied only for the first ULsubframe in a UL transmission burst. The subsequent subframes use thewhole subframe for transmission. The eNB performs scheduling assuming afull subframe transmission although UL transmission can start on otherpositions than subframe boundary. The UE rate matches the TBS toavailable REs based on the starting and ending position. New MCS entriescan be introduced for UL MCS table for partial starting subframe. Thestarting and ending positions of autonomous UL transmission can betransmitted together with PUSCH data from UE to eNB.

The configuration of starting points may be performed according to e.g.one or more of the following:

-   -   The same configuration used for scheduled transmission is        applicable to autonomous transmission without further autonomous        UL specific configuration.    -   eNB configures the starting point for scheduled and autonomous        separately. As a non-limiting example, the eNB can configure the        starting point for autonomous later than scheduled transmission        to provide some priority for scheduled transmission.    -   The starting point is signaled via a common or broadcast signal.        In one embodiment, the starting point is signaled in the common        PDCCH.    -   Assuming that the autonomous UL is enabled using SPS framework,        -   the eNB can configure and activate the starting points as            part of the SPS configuration via higher layer signaling            (RRC).        -   The eNB configures the starting points as part of the SPS            configuration via higher layer signaling (RRC) and activates            all or subset of the starting points via SPS activation on            (e)PDCCH.            Aspect 2: sTTI for UL Transmission on Unlicensed Spectrum

sTTI can be adopted on unlicensed spectrum to facilitate multiplestarting/ending positions for efficient channel access and datatransmission. Examples of sTTI can be 7-symbol based and 2-symbol based.Examples of sTTI patterns are shown in FIG. 7.

In one embodiment, an eNB schedule sTTIs for all UL subframes in atransmission burst on LAA SCell.

In another embodiment, an eNB schedules the first UL transmission in atransmission burst to use sTTIs and subsequent subframes to use fullsubframe scheduling. It can be achieved by using single or multisubframe/TTI scheduling. Besides, both self-carrier scheduling or crosscarrier scheduling can be used.

As one option, the same DCI OB from release 14 can be used to schedulemultiple subframes that may include sTTI. The UE is configured to usesTTI in the first UL subframe of the burst. Given that, the MCS,frequency resource allocation, and other fields of the DCI applies toboth the sTTIs in the first UL subframe and the subsequent subframes inthe burst.

An example is illustrated in FIG. 8. UE performs LBT and follows ULgrant for transmission. If the UE gets the channel on first scheduledsubframe, it starts UL transmission using sTTI on the configured sTTIstarting positions (on subframe n+3 in the example) and then fullsubframe transmissions (for subframe n+4 and n+5 in the example). If theUE doesn't get channel on first scheduled subframe, it shall then usefull subframe transmission with fixed starting point for subsequentsubframes as scheduled by eNB and transmit UL when it gets channel

As another aspect of the embodiment, if the UE does not get channel onthe first scheduled subframe, it shall attempt to transmit in thesubsequent subframe based on the sTTI configuration. This means that theusage of sTTI is not linked to the first scheduled subframe, instead theUE keeps using sTTI until the LBT succeeds then switch to full subframetransmissions for the remaining of the scheduled UL burst.

In yet another embodiment, the sTTI transmissions on LAA Scell aregranted using a new sDCI formats. One format can be used for single sTTIscheduling and another for multi-sTTI scheduling. The new sDCI fromatsinclude all or subset of the following:

-   -   Resource allocations based on Type 3 that is specified for LAA.    -   Channel Access Priority Class    -   Channel Access type    -   PUSCH starting position    -   PUSCH ending symbol

Additionally, the multi-sTTI scheduling sDCI includes number ofscheduled sTTIs or subframes.

In a further embodiment, an eNB schedules the first UL transmission in atransmission burst to use sTTIs and subsequent subframes to use aspect 1as described above. More specifically, subsequent subframes also havemultiple starting positions configured by RRC. If UE gets channel on thefirst subframe, it uses sTTI for first subframe and then full subframetransmission for subsequent subframes. If UE gets channel after thefirst subframe, it transmits on one of the RRC configured startingpositions based on LBT outcome.

To enable more flexibility, the eNB may schedule a UE without a fixedtime relationship between grant and UL transmission. The grantedresources are valid for a certain window of time. Otherwise, the UE doesnot transmit and drops the grant. The first one or more subframes in theUL burst is scheduled based on sTTI to enable multiple start points andthe later subframes are according to the full subframe transmissions.The UE can start preparing the resources at an earlier time, but cannotstart the UL transmission unless it is triggered. The trigger in thiscase is the LBT success. Unlike the previous embodiment, in this case,the UE has the flexibility to always start the UL transmission withsTTI. FIG. 9 shows the behavior in 2 different interference situations.The eNB schedule UE for 4 subframes. The lower edge of the window inwhich the grant is valid is n+4 and the higher edge is n+9. If the UEdoes not get the channel before n+9, the UE drops the grant. The UE casethe flexibility to start the UL burst using sTTI in any subframe withinthe grant window.

In certain other embodiments, an eNB sends two copies of grants for thesame subframe, one based on sTTI and one based on full subframeconfiguration. UE performs UL LBT and decides on which grant to followwhen transmitting UL data depending on LBT outcome.

In another embodiment, both aspects 1 and 2 above are supported. An eNBconfigures aspect 1 when large packet of data needs to be transmittedexpanding several subframes. An eNB configures aspect 2 for small packettransmission. In one example, the selection of an aspect is done via RRCsignaling. In another example, the selection of is done more dynamicallyor flexibly, e.g., using an UL grant.

sTTI can also be adopted for autonomous UL transmission on unlicensedspectrum. Examples of sTTI can be 7-symbol based and 2-symbol based,such as those illustrated in FIG. 7.

In one embodiment, eNB schedules autonomous UL transmission, i.e., theMCS, RB assignment and TBS selection, based on sTTI configuration andsends it to UE when activating autonomous UL. The first subframe ofautonomous UL transmission follows such scheduling configuration byusing the assigned MCS and TBS. For subsequent subframes where a wholesubframe can be used, UE can scale up the TBS accordingly based onavailable REs.

In another embodiment, eNB schedules autonomous UL transmission, i.e.,the MCS, RB assignment and TBS selection, based on sTTI configuration.UE follows such scheduling configuration by using the assigned MCS andTBS for all subframes.

In a further embodiment, eNB schedules autonomous UL transmission basedon both sTTI configuration and full subframe configuration. Two copiesof MCS, RB assignment and TBS are sent to UE. UE selects MCS, RBassignment and TBS based on starting position of autonomous ULtransmission for a certain subframe. I.e., if it is partial startingsubframe, the MCS/TBS based on sTTI is applied for transmission;otherwise, the MCS/TBS based on full subframe is applied fortransmission.

In another embodiment, the eNB configures a UE to use sTTI configurationbased on a certain frame periodicity. That is, the UE is configured withone or more subframe that can transmit autonomous UL transmission usingsTTI every X subframes. Given that, the UE benefits from additionalstarting points only within the subframes that are configured with sTTItransmissions. In addition, it minimizes eNB blind detection efforts.

Assuming that autonomous UL is enabled using SPS framework, the eNB canenable or disable the multiple starting points depending on the DLcontrol signaling used. For instance, to enable more starting pointsbased on sTTI configuration, the eNB sends the SPS activation command onsPDCCH. Otherwise, if SPS command is sent on PDCCH, the UE does nottransmit according to the sTTI configuration. If SPS activation is senton both PDCCH and sPDCCH, the UE has the flexibility to transmitaccording to a full subframe of sTTI configuration depending on LBToutcome.

Alternatively, higher layer configuration (RRC) can be used to activateUL sTTI on SPS resources. As an example, the UE may be configured to usesTTI configuration on SPS resources based on a certain frameperiodicity, for instance “X” subframes configured with sTTI every “Y”subframes. The UE can still attempt to do autonomous UL outside thosesubframes but not using the sTTI configuration.

The described embodiments may be implemented in any appropriate type ofcommunication system supporting any suitable communication standards andusing any suitable components. As one example, certain embodiments maybe implemented in a communication system such as that illustrated inFIG. 1. Although certain embodiments are described with respect to LTEsystems and related terminology, the disclosed concepts are not limitedto LTE or a 3GPP system. Additionally, although reference may be made tothe term “cell”, the described concepts may also apply in othercontexts, such as beams used in Fifth Generation (5G) systems, forinstance.

Referring to FIG. 10, a communication system 100 comprises a pluralityof wireless communication devices 105 (e.g., UEs, machine typecommunication [MTC]/machine-to-machine [M2M] UEs) and a plurality ofradio access nodes 110 (e.g., eNodeBs or other base stations).Communication system 100 is organized into cells 115, which areconnected to a core network 120 via corresponding radio access nodes110. Radio access nodes 110 are capable of communicating with wirelesscommunication devices 105 along with any additional elements suitable tosupport communication between wireless communication devices or betweena wireless communication device and another communication device (suchas a landline telephone).

Although wireless communication devices 105 may represent communicationdevices that include any suitable combination of hardware and/orsoftware, these wireless communication devices may, in certainembodiments, represent devices such as those illustrated in greaterdetail by FIGS. 11A and 11B. Similarly, although the illustrated radioaccess node may represent network nodes that include any suitablecombination of hardware and/or software, these nodes may, in particularembodiments, represent devices such those illustrated in greater detailby FIGS. 12A, 12B and 13.

Referring to FIG. 11A, a wireless communication device 200A comprises aprocessor 205 (e.g., Central Processing Units [CPUs], ApplicationSpecific Integrated Circuits [ASICs], Field Programmable Gate Arrays[FPGAs], and/or the like), a memory 210, a transceiver 215, and anantenna 220. In certain embodiments, some or all of the functionalitydescribed as being provided by UEs, MTC or M2M devices, and/or any othertypes of wireless communication devices may be provided by the deviceprocessor executing instructions stored on a computer-readable medium,such as memory 210. Alternative embodiments may include additionalcomponents beyond those shown in FIG. 2A that may be responsible forproviding certain aspects of the device's functionality, including anyof the functionality described herein.

Referring to FIG. 11B, a wireless communication device 200B comprises atleast one module 225 configured to perform one or more correspondingfunctions. Examples of such functions include various method steps orcombinations of method steps as described herein with reference towireless communication device(s). In general, a module may comprise anysuitable combination of software and/or hardware configured to performthe corresponding function. For instance, in some embodiments a modulecomprises software configured to perform a corresponding function whenexecuted on an associated platform, such as that illustrated in FIG.11A.

Referring to FIG. 12A, a radio access node 300A comprises a controlsystem 320 that comprises a node processor 305 (e.g., Central ProcessingUnits (CPUs), Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), and/or the like), memory 310, and anetwork interface 315. In addition, radio access node 300A comprises atleast one radio unit 325 comprising at least one transmitter 335 and atleast one receiver coupled to at least one antenna 330. In someembodiments, radio unit 325 is external to control system 320 andconnected to control system 320 via, e.g., a wired connection (e.g., anoptical cable). However, in some other embodiments, radio unit 325 andpotentially the antenna 330 are integrated together with control system320. Node processor 305 operates to provide at least one function 345 ofradio access node 300A as described herein. In some embodiments, thefunction(s) are implemented in software that is stored, e.g., in thememory 310 and executed by node processor 305.

In certain embodiments, some or all of the functionality described asbeing provided by a base station, a node B, an enodeB, and/or any othertype of network node may be provided by node processor 305 executinginstructions stored on a computer-readable medium, such as memory 310shown in FIG. 3A. Alternative embodiments of radio access node 300 maycomprise additional components to provide additional functionality, suchas the functionality described herein and/or related supportingfunctionality.

Referring to FIG. 12B, a radio access node 300B comprises at least onemodule 350 configured to perform one or more corresponding functions.Examples of such functions include various method steps or combinationsof method steps as described herein with reference to radio accessnode(s). In general, a module may comprise any suitable combination ofsoftware and/or hardware configured to perform the correspondingfunction. For instance, in some embodiments a module comprises softwareconfigured to perform a corresponding function when executed on anassociated platform, such as that illustrated in FIG. 12A.

FIG. 13 is a block diagram that illustrates a virtualized radio accessnode 400 according to an embodiment of the disclosed subject matter. Theconcepts described in relation to FIG. 4 may be similarly applied toother types of network nodes. Further, other types of network nodes mayhave similar virtualized architectures. As used herein, the term“virtualized radio access node” refers to an implementation of a radioaccess node in which at least a portion of the functionality of theradio access node is implemented as a virtual component(s) (e.g., via avirtual machine(s) executing on a physical processing node(s) in anetwork(s)).

Referring to FIG. 13, radio access node 400 comprises control system 320as described in relation to FIG. 12A.

Control system 320 is connected to one or more processing nodes 420coupled to or included as part of a network(s) 425 via network interface315. Each processing node 420 comprises one or more processors 405(e.g., CPUs, ASICs, FPGAs, and/or the like), memory 410, and a networkinterface 415.

In this example, functions 345 of radio access node 300A describedherein are implemented at the one or more processing nodes 420 ordistributed across control system 320 and the one or more processingnodes 420 in any desired manner. In some embodiments, some or all of thefunctions 345 of radio access node 300A described herein are implementedas virtual components executed by one or more virtual machinesimplemented in a virtual environment(s) hosted by processing node(s)420. As will be appreciated by one of ordinary skill in the art,additional signaling or communication between processing node(s) 420 andcontrol system 320 is used in order to carry out at least some of thedesired functions 345. As indicated by dotted lines, in some embodimentscontrol system 320 may be omitted, in which case the radio unit(s) 325communicate directly with the processing node(s) 420 via an appropriatenetwork interface(s).

In some embodiments, a computer program comprises instructions which,when executed by at least one processor, causes at least one processorto carry out the functionality of a radio access node (e.g., radioaccess node 110 or 300A) or another node (e.g., processing node 420)implementing one or more of the functions of the radio access node in avirtual environment according to any of the embodiments describedherein.

FIGS. 14-15 illustrate various methods of operating a wirelesscommunication device according to embodiments of the disclosed subjectmatter. These methods could be performed by an apparatus such as thatillustrated in any of FIGS. 10-13, for instance. Additionally, thesemethods could be performed in conjunction with any of variousalternative features as described above, such as various alternativetime transmission interval configurations, subframe configurations,timing arrangements, signaling procedures, etc.

Referring to FIG. 14, a method 1400 comprises identifying multiple setsof candidate start and end positions for uplink (UL) transmission inunlicensed spectrum (S1405), selecting at least one set of start and endpositions from among the candidates, based on an outcome of alisten-before-talk (LBT) procedure performed with respect to theunlicensed spectrum (S1410), and performing UL transmission in theunlicensed spectrum using the selected at least one set of start and endpositions (S1415). In this and other embodiments, the identification ofmultiple sets of candidate start positions may include e.g. receivinginformation from a radio access node, reading information from memory,etc. The selecting may be performed in any of various alternative waysas described above in relation to FIGS. 6-9, for instance. Theperforming of UL transmission may comprise e.g. transmitting informationusing defined resources as described above.

Referring to FIG. 15, a method 1500 comprises identifying a first startposition for performing uplink (UL) transmission in unlicensed spectrumduring a first transmission time interval (TTI) (S1505), performing ULtransmission in the first TTI according to the first start position(S1510), identifying a second start position for performing ULtransmission in unlicensed spectrum during a second TTI, wherein thefirst and second start positions correspond to different symbol offsetswithin the respective first and second TTIs (S1515), and performing ULtransmission in the second TTI according to the second start position(S1520).

FIG. 16 illustrates a method of operating a radio access node accordingto an embodiment of the disclosed subject matter. This method could beperformed by an apparatus such as that illustrated in any of FIG. 10, 12or 13, for instance. Additionally, this method could be performed inconjunction with any of various alternative features as described above,such as various alternative time transmission interval configurations,subframe configurations, timing arrangements, signaling procedures, etc.

Referring to FIG. 16, a method 1600 comprises identifying a first startposition for an uplink (UL) transmission performed in unlicensedspectrum during a first transmission time interval (TTI) (S1605),receiving the UL transmission in the first TTI according to the firststart position (S1610), identifying a second start position for an ULtransmission performed in unlicensed spectrum during a second TTI,wherein the first and second start positions correspond to differentsymbol offsets within the respective first and second TTIs (S1615), andreceiving the UL transmission in the second TTI according to the secondstart position (S1620).

The following is a list of acronyms that may be used in this writtendescription.

BSR Buffer Status Request

CC Component Carrier

CCA Clear Channel Assessment

CQI Channel Quality Information

CRC Cyclic Redundancy Check

DCI Downlink Control Information

DL Downlink

DMTC DRS Measurement Timing Configuration

DRS Discovery Reference Signal

eNB evolved NodeB, base station

UE User Equipment

UL Uplink

LAA Licensed-Assisted Access

SCell Secondary Cell

STA Station

LBT Listen-before-talk

LTE-U LTE in Unlicensed Spectrum

PDCCH Physical Downlink Control Channel

PMI Precoding Matrix Indicator

PUSCH Physical Uplink Shared Channel

RAT Radio Access Technology

RNTI Radio Network Temporary Identifier

TXOP Transmission Opportunity

UL Uplink

sTTI Shortened TTI

While the disclosed subject matter has been presented above withreference to various embodiments, it will be understood that variouschanges in form and details may be made to the described embodimentswithout departing from the overall scope of the disclosed subjectmatter.

The invention claimed is:
 1. A method of operating a wirelesscommunication device, comprising: identifying a first start position forperforming uplink (UL) transmission in unlicensed spectrum during afirst transmission time interval (TTI); performing UL transmission inthe first TTI according to the first start position; identifying asecond start position for performing UL transmission in unlicensedspectrum during a second TTI, wherein the first and second startpositions correspond to different symbol offsets within the respectivefirst and second TTIs; and performing UL transmission in the second TTIaccording to the second start position; wherein identifying the firststart position comprises performing a first listen-before-talk (LBT)procedure, and selecting the first start position in response to asuccess of the first LBT procedure; and wherein identifying the secondstart position comprises performing a second LBT procedure, andselecting the second start position as a consequence of a failure of thesecond LBT procedure.
 2. The method of claim 1, wherein a symbol offsetfor the first start position corresponds to a symbol 0, and a symboloffset for the second start position corresponds to a symbol
 7. 3. Themethod of claim 1, wherein identifying the second start positioncomprises receiving an UL grant indicating that a symbol offset for thesecond start position corresponds to a symbol
 7. 4. The method of claim3, further comprising rate matching the UL transmission to be performedin the second TTI based on available resource elements (REs) for thesecond start position.
 5. The method of claim 1, further comprising:identifying a first end position for performing the UL transmission thefirst TTI; performing the UL transmission in the first TTI according tothe first end position; identifying a second end position for performingthe UL transmission the second TTI, wherein the first and second endpositions correspond to different symbol offsets within the respectivefirst and second TTIs; and performing the UL transmission in the secondTTI according to the second end position.
 6. The method of claim 5,wherein identifying the first end position comprises receiving an ULgrant indicating the first end position.
 7. The method of claim 1,wherein the first TTI is a short TTI (sTTI) and the second TTI is afull-subframe or multi-subframe TTI.
 8. The method of claim 7, whereinthe sTTI is a 7-symbol based sTTI or a 2-symbol based sTTI.
 9. Themethod of claim 1, further comprising selecting different modulation andcoding schemes (MCSs) for the UL transmissions in the first and secondTTIs according to the respective first and second start positions. 10.The method of claim 9, wherein the second start position has a largersymbol offset than the first start position, and the selected MCS forthe UL transmission in the second TTI has a higher modulation order thanthe selected MCS for the UL transmission in the first TTI.
 11. A methodof operating a radio access node, comprising: identifying a first startposition for an uplink (UL) transmission performed in unlicensedspectrum during a first transmission time interval (TTI); receiving theUL transmission in the first TTI according to the first start position;identifying a second start position for an UL transmission performed inunlicensed spectrum during a second TTI, wherein the first and secondstart positions correspond to different symbol offsets within therespective first and second TTIs; and receiving the UL transmission inthe second TTI according to the second start position; wherein the firststart position is identified in response to a first listen-before-talk(LBT) procedure successfully gaining access to a communication channel,and the second start position is identified in response to a second LBTprocedure failing to gain access to the communication channel.
 12. Themethod of claim 11, wherein a symbol offset for the first start positioncorresponds to a symbol 0, and a symbol offset of the second startposition corresponds to a symbol
 7. 13. The method of claim 11, furthercomprising transmitting an UL grant to a user equipment (UE) to indicatethat a symbol offset for the second start position corresponds to asymbol
 7. 14. The method of claim 11, further comprising: identifying afirst end position for the UL transmission the first TTI; receiving theUL transmission in the first TTI according to the first end position;identifying a second end position for the UL transmission the secondTTI, wherein the first and second end positions correspond to differentsymbol offsets within the respective first and second TTIs; andreceiving the UL transmission in the second TTI according to the secondend position.
 15. The method of claim 14, further comprisingtransmitting an UL grant indicating the first end position to a userequipment (UE).
 16. The method of claim 15, wherein the first TTI is ashort TTI (sTTI) and the second TTI is a full-subframe or multi-subframeTTI.
 17. The method of claim 16, wherein the sTTI is a 7-symbol basedsTTI or a 2-symbol based sTTI.
 18. A wireless communication device,comprising: processing circuitry configured to: identify a first startposition for performing uplink (UL) transmission in unlicensed spectrumduring a first transmission time interval; perform UL transmission inthe first transmission time interval (TTI) according to the first startposition; identify a second start position for performing ULtransmission in unlicensed spectrum during a second TTI, wherein thefirst and second start positions correspond to different symbol offsetswithin the respective first and second TTIs; and perform UL transmissionin the second TTI according to the second start position; whereinidentifying the first start position comprises performing a firstlisten-before-talk (LBT) procedure, and selecting the first startposition in response to a success of the first LBT procedure; andwherein identifying the second start position comprises performing asecond LBT procedure, and selecting the second start position as aconsequence of a failure of the second LBT procedure.
 19. The wirelesscommunication device of claim 18, wherein a symbol offset for the firststart position corresponds to a symbol 0, and a symbol offset for thesecond start position corresponds to a symbol
 7. 20. The wirelesscommunication device of claim 18, wherein identifying the second startposition comprises receiving an UL grant indicating that a symbol offsetfor the second start position corresponds to a symbol
 7. 21. Thewireless communication device of claim 20, wherein the processingcircuitry is further configured to rate match the UL transmission to beperformed in the second TTI based on available resource elements (REs)for the second start position.
 22. The wireless communication device ofclaim 18, wherein the processing circuitry is further configured to:identify a first end position for performing the UL transmission thefirst TTI; perform the UL transmission in the first TTI according to thefirst end position; identify a second end position for performing the ULtransmission the second TTI, wherein the first and second end positionscorrespond to different symbol offsets within the respective first andsecond TTIs; and perform the UL transmission in the second TTI accordingto the second end position.
 23. The wireless communication device ofclaim 22, wherein identifying the first end position comprises receivingan UL grant indicating the first end position.
 24. The wirelesscommunication device of claim 18, wherein the first TTI is a short TTI(sTTI) and the second TTI is a full-subframe or multi-subframe TTI. 25.The wireless communication device of claim 24, wherein the sTTI is a7-symbol based sTTI or a 2-symbol based sTTI.
 26. The wirelesscommunication device of claim 18, wherein the processing circuitry isfurther configured to select different modulation and coding schemes(MCSs) for the UL transmissions in the first and second TTIs accordingto the respective first and second start positions.
 27. The wirelesscommunication device of claim 26, wherein the second start position hasa larger symbol offset than the first start position, and the selectedMCS for the UL transmission in the second TTI has a higher modulationorder than the selected MCS for the UL transmission in the first TTI.28. A radio access node, comprising: processing circuitry configured to:identify a first start position for an uplink (UL) transmissionperformed in unlicensed spectrum during a first transmission timeinterval (TTI); receive the UL transmission in the first TTI accordingto the first start position; identify a second start position for an ULtransmission performed in unlicensed spectrum during a second TTI,wherein the first and second start positions correspond to differentsymbol offsets within the respective first and second TTIs; and receivethe UL transmission in the second TTI according to the second startposition; wherein the first start position is identified in response toa first listen-before-talk (LBT) procedure successfully gaining accessto a communication channel, and the second start position is identifiedin response to a second LBT procedure failing to gain access to thecommunication channel.
 29. The radio access node of claim 28, wherein asymbol offset for the first start position corresponds to a symbol 0,and a symbol offset of the second start position corresponds to a symbol7.
 30. The radio access node of claim 28, wherein the processingcircuitry is further configured to transmit an UL grant to a userequipment (UE) to indicate that a symbol offset for the second startposition corresponds to a symbol
 7. 31. The radio access node of claim28, wherein the processing circuitry is further configured to: identifya first end position for the UL transmission the first TTI; receive theUL transmission in the first TTI according to the first end position;identify a second end position for the UL transmission the second TTI,wherein the first and second end positions correspond to differentsymbol offsets within the respective first and second TTIs; and receivethe UL transmission in the second TTI according to the second endposition.
 32. The radio access node of claim 31, wherein the processingcircuitry is further configured to transmit an UL grant indicating thefirst end position to a user equipment (UE).
 33. The radio access nodeof claim 32, wherein the first TTI is a short TTI (sTTI) and the secondTTI is a full-subframe or multi-subframe TTI.
 34. The radio access nodeof claim 33, wherein the sTTI is a 7-symbol based sTTI or a 2-symbolbased sTTI.